Untitled

#include <stdio.h>
#include <stdlib.h>
#include "ilist_destructive.h"

// The ilist ADT is a pointer to this secret struct
struct ilist_ADT {
   struct ilist_ADT * rest;
   int first;
   int length;
   struct ilist_ADT * last;
};
   ilist iempty(){
   return NULL;
   }
   
   int iempty_huh(ilist il){
   return il == iempty();
   }
   
   int ifirst(ilist il){
   return il->first;
   }
    
   ilist icons_destroy(int in, ilist il){
   if(iempty_huh(il)) {
                ilist end = malloc(sizeof(struct ilist_ADT));
                end->rest = iempty();
                end->length = 1;
                end->first = in;
                end->last = end;
                return end;
        }
    ilist temp = malloc(sizeof(struct ilist_ADT));
    temp->length = il->length;
    temp->first = il->first;
    temp->rest = il->rest;
    temp->last = il->last;
    il->last = temp->last;
    il->length = ilength(il) + 1;
    il->rest = temp;
    il->first = in;
    return il;
   }
   // returns an ilist with in added as the first element of il
   // references to il cease to be valid ilists
   // the result must eventually be consumed by one of:
   //     icons_destroy, irest_destroy, idelete
   
   ilist irest_destroy(ilist il){
   ilist temp = il->rest;
   free (il);
   return temp;
   }
   // modifies il to remove the first element, and returns the modified ilist
   // frees the memory associated with the first element
   // references to il cease to be valid ilists
   // the result (if non-empty) must eventually be consumed by one of:
   //     icons_destroy, irest_destroy, idelete
   
   ilist icopy(ilist il){
   if (il== iempty())
   {return iempty();}
   ilist head = malloc (sizeof(struct ilist_ADT));
   head->first = il->first;
   head->length = il->length;
   head->rest = iempty();
   ilist lstend = head;
   
   for (ilist a = il->rest; a!=iempty(); a = a->rest){
   ilist temp = malloc (sizeof(struct ilist_ADT));
   temp->first = a->first;
   temp->length = a->length;
   temp->rest = iempty();
   lstend->rest = temp;
   lstend = temp;
   }
   return head;   
   }
   // returns a new copy of il that continues to be a valid
   // ilist with the same elements even when il is destroyed
   // the result must eventually be consumed by one of:
   //     icons_destroy, irest_destroy, idelete

   int ilength(ilist il)
   {
   if (iempty_huh(il))
   {
   return 0;
   }
   else
   {
   return il->length;
   }
}
   // computes the number of elements in il

   void idelete(ilist il){
      while (il != iempty()) { 
      ilist next = il->rest;
      free(il);
      il = next;
   }
   }
   //    frees the storage for ilist
   //    all further references to il become invalid
   //    NOTE: every ilist created by icons_destroy or
   //          irest_destroy or icopy  must eventually be destroyed
   //          by being consumed by icons_destroy or
   //          irest_destroy or idelete
   

ilist iappend_destroy (ilist il1, ilist il2){

if (iempty_huh(il1)){
return il2;
}
if (iempty_huh(il2)){
return il1;
}

if (il1 == il2){
il2 = icopy(il1);
}

il1->last->rest = il2;
return il1;
}